The proposal involves the development of a system for the temporally and spatially controlled conditional silencing of retinal ganglion cells in zebrafish. The system, based on the P[switch] system in Drosophila, will be of potential use to a wide variety of studies throughout the zebrafish nervous system. Specifically, the later aims of this proposal will involve analyzing the importance of activity and competition for the establishment of the retinotopic map, and determining a critical period for this activity in zebrafish. Finally, the constantly developing retinotectal connections in adult zebrafish allow for the analysis of activity in neuronal plasticity. All of these issues will be approached by blocking activity in subsets of retinal ganglion cells for discrete periods of time during development, and observing the effects on the structures of individual neurons, and on the retinotopic map as a whole. These experiments have the potential to provide information on the roles of activity and competition on neural development in vertebrates